Dutch coastguard ships and helicopters scrambled Thursday to search for a missing fishing trawler after it sent out an automated distress signal in the North Sea, the coastguard said.

The small fishing vessel Lummetje activated an automated emergency signal around 5:45 am a few miles off the coast of the northern Dutch island of Texel, the coastguard said on its website. Two people were on board.

"A large number of ships are at the scene, including ships of the Royal Dutch Sea Rescue Institute, and two helicopters... have been alerted," the coastguard said.

"The helicopter saw a raft drifting in the area, but there was nobody on board," it said, adding that conditions at the scene were unusually rough, with strong winds and waves of up to two metres (six feet).

A Dutch navy mine hunter, the Makkum, has also joined the search.

Attempts to contact the trawler, which is based in the small fishing port of Urk, were unsuccessful, the coastguard said.

The waters of the busy sea route off the Dutch coast are normally calm.

Early this year, the world's largest container ship, the MSC Zoe, lost hundreds of containers in a storm off the Netherlands' Wadden islands, of which Texel is the largest.